I suggest by know just move the current Promise implementation to sysapps/common and make it a separate module that can be include with via requireNative(). Again, it will work just fine with Android.

This would be the first step. Later we can investigate what is the best Promise implementation to use like @kenchris suggest. Let's do it incrementally, I have a bug for tracking this -> https://crosswalk-project.org/jira/browse/XWALK-339